asterix-runtime/src/main/java/edu/uci/ics/asterix/runtime/evaluators/functions/IsNullDescriptor.java

package edu.uci.ics.asterix.runtime.evaluators.functions;

import java.io.DataOutput;

import edu.uci.ics.asterix.dataflow.data.nontagged.serde.AObjectSerializerDeserializer;
import edu.uci.ics.asterix.om.base.ABoolean;
import edu.uci.ics.asterix.om.functions.IFunctionDescriptor;
import edu.uci.ics.asterix.om.functions.IFunctionDescriptorFactory;
import edu.uci.ics.asterix.om.types.ATypeTag;
import edu.uci.ics.asterix.runtime.evaluators.base.AbstractScalarFunctionDynamicDescriptor;
import edu.uci.ics.hyracks.algebricks.common.exceptions.AlgebricksException;
import edu.uci.ics.hyracks.algebricks.core.algebra.functions.AlgebricksBuiltinFunctions;
import edu.uci.ics.hyracks.algebricks.core.algebra.functions.FunctionIdentifier;
import edu.uci.ics.hyracks.algebricks.runtime.base.ICopyEvaluator;
import edu.uci.ics.hyracks.algebricks.runtime.base.ICopyEvaluatorFactory;
import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
import edu.uci.ics.hyracks.data.std.api.IDataOutputProvider;
import edu.uci.ics.hyracks.data.std.util.ArrayBackedValueStorage;
import edu.uci.ics.hyracks.dataflow.common.data.accessors.IFrameTupleReference;

public class IsNullDescriptor extends AbstractScalarFunctionDynamicDescriptor {

    private static final long serialVersionUID = 1L;

    public final static FunctionIdentifier FID = new FunctionIdentifier(AlgebricksBuiltinFunctions.ALGEBRICKS_NS,
            "is-null", 1);
    private final static byte SER_NULL_TYPE_TAG = ATypeTag.NULL.serialize();
    public static final IFunctionDescriptorFactory FACTORY = new IFunctionDescriptorFactory() {
        public IFunctionDescriptor createFunctionDescriptor() {
            return new IsNullDescriptor();
        }
    };

    @Override
    public ICopyEvaluatorFactory createEvaluatorFactory(final ICopyEvaluatorFactory[] args) throws AlgebricksException {
        return new ICopyEvaluatorFactory() {

            private static final long serialVersionUID = 1L;

            @Override
            public ICopyEvaluator createEvaluator(final IDataOutputProvider output) throws AlgebricksException {
                return new ICopyEvaluator() {

                    private DataOutput out = output.getDataOutput();
                    private ArrayBackedValueStorage argOut = new ArrayBackedValueStorage();
                    private ICopyEvaluator eval = args[0].createEvaluator(argOut);

                    @Override
                    public void evaluate(IFrameTupleReference tuple) throws AlgebricksException {
                        argOut.reset();
                        eval.evaluate(tuple);
                        boolean isNull = argOut.getByteArray()[argOut.getStartOffset()] == SER_NULL_TYPE_TAG;
                        ABoolean res = isNull ? ABoolean.TRUE : ABoolean.FALSE;
                        try {
                            AObjectSerializerDeserializer.INSTANCE.serialize(res, out);
                        } catch (HyracksDataException e) {
                            throw new AlgebricksException(e);
                        }
                    }
                };
            }
        };
    }

    @Override
    public FunctionIdentifier getIdentifier() {
        return FID;
    }

}